Zimbabwe police fired tear gas and water cannons to break up an opposition protest in the capital Harare, despite a court order not to interfere with the demonstration.
The police action led to running battles with protesters who threw rocks at police, burned tires and set market stalls on fire.
The confrontation began Monday when police in riot gear occupied the venue where protesters planned to demonstrate, and told them to leave as they arrived for the march. When some of the protesters refused to comply, police fired tear gas and water cannons.
Morgan Tsvangirai, opposition leader and head of the Movement for Democratic Change, and former Vice President Joice Mujuru led the planned demonstration, a rare occurrence for the country's fractured opposition to join in a single action.
More than 18 opposition parties and civic organizations came together for the planned march, which organizers estimated would draw tens of thousands of people.
"The people's anger is very deep," Tsvangirai said. "Today's brutal suppression of the people will not stop them from exercising their rights."
The opposition coalition has promised to demonstrate again next Friday.
Demonstrators are demanding electoral reforms before 2018 when President Robert Mugabe, who is 92, will seek re-election. Mugabe has led Zimbabwe since independence from Britain in 1980.